Add support for Introducer

depends on bitmask-core#14 (closed)

Features we want to have:

People can add a introducer

• by clicking a link (desktop registers a url scheme)
• by scanning a qr code
• by entering the introducer url

GUI

• you can add the introducer by the mechanisms described above
• in the settings, you can:
• see the introducer, delete it, disable/enable it
• if you add another one introducer, the first one will be deleted (only one can be stored)

Data

• Introducer must be stored in the config file

For the first Poc, we want to use an obfs4 bridge. Therefore, we need a menshen instance behind a obfs4 bridge. There are also a lot of UI todos. I hope @jkito you can take care of it.

UPDATE: for the first PoC - A user can enter a obsvpnintro// url instead of entering a provider URL. This simplifies the whole thing a bit in the first step.